Electroplating of copper is a common technique in the manufacture of electronic components such as printed circuit boards and IC substrates. Different types of features in a multilayer laminate such as blind micro vias (BMVs) and recessed structures in a patterned resist layer need to be completely filled with copper. Copper filled recessed structures in patterned resist layers are referred herein as trenches.
With an ongoing miniaturization of such features in electronic components electroplating of copper becomes more demanding. The diameter of BMVs is getting smaller and at the same time their aspect ratio is increased. The line width and interline distance of trenches is reduced to 50 μm or even below 10 or 5 μm.
Accordingly, the requirements for BMV filling with copper are increased. At the same time, also the requirements for the cross-sectional shape of trenches are increased. Cross-sectional trench shapes such as ski-slope shaped trenches (2) (FIG. 1) and round shaped trenches (3) (FIG. 2) (round edges) are not sufficient anymore in terms of e.g. current propagation. A rectangular cross-sectional shape of trenches (4) on a substrate surface (1) is desired (FIG. 3).
It is also highly desired for economical reasons to electroplate different features such as BMVss and trenches in one step while fulfilling the required filling quality of BMVss and obtaining the rectangular cross-sectional shape of trenches.
Filling of BMVs' with copper by electroplating under reverse pulse plating conditions is for example disclosed in US 2009/0301889 A1. The method disclosed in this document leads to a sufficient filling of BMVs' with copper but the cross-sectional line shapes of trenches plated at the same time is not always sufficient.